A known vehicle occupant restraint system includes a length of seat belt webbing wound on a spool of a retractor. The seat belt webbing is extensible about a vehicle occupant to help protect the occupant in the event of a vehicle collision. The retractor includes a pair of ratchet wheels fixed for rotation with the spool. A lock pawl is pivotable from an unlocked position to a locked position by a vehicle deceleration sensing device. The lock pawl is also pivotable from the unlocked position to the locked position by a webbing acceleration sensing device which senses the acceleration at which the seat belt webbing is withdrawn from the spool. In the locked position, the lock pawl engages teeth on the ratchet wheels to prevent payout of the seat belt webbing.
The vehicle deceleration sensing device and the webbing acceleration sensing device are usually enclosed underneath a cover member to prevent the ingress of dirt into the sensing devices. The vehicle deceleration sensing device and the webbing acceleration sensing device typically include numerous movable components which can vibrate, generating audible noise which may be objectionable to the vehicle occupants.